We got a question today from a customer who says centipedes are damaging the roots of his squash plants. "I noticed a bunch (maybe 50) centipedes on the roots of my squash plants."
First of all, they are probably millipedes. Centipedes (which have one set of legs per segment) would be eating other insects. Millipedes (two sets of legs per segment) are sometimes found in large numbers in moist garden soil that contains a lot of organic matter because they feed mainly on decomposing organic matter. Sometimes they will damage young seedlings, but usually the problem starts otherwise; and the millipedes are eating the damaged, rotting stems and roots. For instance, if your soil is staying too wet or if you’re watering late in the day, the problem may have started with root rot. Or if you have squash vine borers, the millipedes will feed on the damaged stems. If you do think your problem is starting and ending with millipedes, I’d apply some diatomaceous earth (or Permaguard which is diatomaceous earth with pyrethrin) around the base of the plant and wherever it touches the soil. Do not use more than you have to however, as this will affect your earthworms also.
In any case, count on squash vine borers to cause problems with this crop. I recommend drenching the stems of your squash plants (especially at the base) with Thuricide (liquid Bt) at least a couple times per week and more if you have time. The moths will lay eggs at the base of your plants, but they will be protected when the larva hatches if it has to eat its way through Bt to get into the stem (the borers/larva will be dead before they can do any real damage). Keep an eye out for the moths which are active during the day. As you can see from the photo, they’re pretty distinctive. Kill them whenever you can, and increase the Bt treatments while they’re active.
One more caution about watering. You’ll avoid a lot of problems simply by watering early and giving the plants time to dry before evening, but be aware that overhead irrigation will wash the Bt off the squash stems. Drip irrigation solves this problem and (since it does not get the foliage wet) relieves the necessity to water early. If this is not an option, you may want to increase the number of Bt treatments to replace product that has been washed off.
Frankly if I did not love yellow crookneck squash and zucchini as much as I do (and if homegrown squash did not taste so much better than what you get at the store), I would not go to this much trouble. But I do (and it does), so it’s definitely worth the extra work.